Gelatin coating composition



atented Nov. 13, 1945 'lA'l'ES GELATIN CGATWG fiDOS Donald R. Swan, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y a corporation of New .lersey NolDrawing. Application August 3, 1940,

Serial No. 351,091

1 Claim.

This invention relates-t a gelatin coating com position particularly adapted for photographic uses in which a small amount of methyl cellulose is mixed with 'the gelatin to improve the characteristics of the solution.

In the photographic art, gelatin compositions are widely usedeither as photosensitive emulsions,

as over coatings or as backings for photographic film. In applying such compositions it is desirable that the formation of air bubbles in the composition bereduced to a minimum and'that the coating spread uniformly over the surface being coated.

One object of my invention is to provide a gelatin coating composition in which the formation of air bubbles is minimized. Another object of my roe-12s) composition may vary within wide limits. I have tried the methyl celluloses of the types designated commercially as low viscosity, medium viscosity, high viscosity and extra high viscosity, in my composition and all these types have been suitable.

, For instance four aqueous gelatin solutions of plied to a surface to be coated. Other objects of my invention will appear herein.

I have found that if an amount of methyl cellulose up to 20% of the total solids is incorporated in an aqueous solution of gelatin that the forma tion of air bubbles therein is minimized, the spreading properties are enhanced and the setting time of the coating isconsiderably reduced.

My invention particularly includes compositions used in coating photographic film or film base in which a warm gelatin coating is applied to a surface. For instance if a warm gelatin overcoating is applied on to a wet, chilled photographic emul- I sion there is ordinarily adecided tendency to form air bubbles. With a gelatin composition as speci fied herein the formation of ,air bubbles does "not occur in coating it with a-warm gelatin solution. In its broader aspects my invention comprises '7 /z% concentration were prepared and methyl cellulose at the rate of 15 gms. per pound of gelatin were incorporated in each, each receiving a different one "of the viscosity types given above. A'coating was made from each at a temperature of 95-100" F. The setting time of each was at most half that of a gelatin coating from a gelatin solution of the same concentration containing no methyl cellulose. The composition containing the extra-high viscosity methyl cellulose, exhibite the shortest setting time.

It is desirable in making up coating compositions in accordance with my invention that it be filtered before applying to a surface if the maximum clarity is desirable. This however is left to the discretion of the individualoperator who may judge from the appearance of the coating composition whether or not filtering is necessary.

As pointed out above my coating composition ing for any purpose, my coating composition may' be applied directly thereto and will exhibit good adherence. "My composition is also useful as a gelatin coating compositions composed of a solution of about 13-10% of gelatin in water plus methyl cellulose in an amount up to 20% (preferably 520%) based-on the total weight of solids Dresent. The methyl 'celluloseis of the water-soluble type and has a methoxyl content of 16+28%. This composition may be applied in warm cond tion directly upon a photosensitive emulsion. This composition spreads more readily than a gelatin solution of the same concentration and is therefore readily applied.

The coating composition is preferably made up at an elevated temperature such as 'l00-120 F. in view of the greater facility with which gelatin dissolves at an elevated temperature. The composition is kept at 90-120 F. for the coating operation so as to assure good fluidity. After applying to a surface, the. coating layer is set b cooling preferably by subjecting it to a current 0 cold air. Although any current of air of room carrier for the photosensitive element in photo graphic emulsions such as to carry the silver halide which is usually employed therein. Due to its improved spreading properties the coating of a gelatin photosensitive emulsion. containing methit is unnecessary and usually undesirable to usemore than 0.5%-2% of the methyl cellulose (based on the weight of the gelatin). Eor ordinary purposes. however, the coating compositions specified herein are satisfactory in the transmittal of light therethrough. A

I claim:

A coating composition for photo raphic purnoses adapted to give coatings of high transparency. consisting of an aqueous solution of gelatin of 3-10% concentration. which solution sets at temperature or below may be useful, I have found that air having a temperature near to (but above the freezing point of water (32 F.) is most desirable.

The viscosity of the methyl. cellulose used in any content of 16-28%.

' DONALD R. SWAN. 

